Heat roller for fixing apparatus

ABSTRACT

A heat roller for a fixing apparatus includes a conductive cylindrical roller body, and a resistance heater installed in the roller body. Caps at each end of the heat roller have electrodes for supplying a current to the resistance heater. A fastening means confines at least one cap to prevent the cap from being axially separated from the roller body and to substantially prevent the cap from being idled in the roller body.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(a) of KoreanPatent Application No. 2005-54781, filed on Jun. 24, 2005, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fixing apparatus for an image formingapparatus. More particularly, the present invention relates to a heatroller for a fixing apparatus provided with a key capable ofsubstantially preventing the heat roller from slipping at a roller cap.

2. Description of the Related Art

An image forming apparatus, such as a laser printer, a duplicator andother similar apparatuses, prints a desired image on a recording mediumthrough processes of charging, exposing, transferring and fixing. Amongthese processes, the fixing process is a process of fixing a toner imagetransferred to the recording medium by applying heat and pressure, andis generally performed by a fixing apparatus including a pair ofrollers.

One of the pair of rollers of the fixing apparatus is a pressure rollerand the other roller is a heat roller. FIG. 1 illustrates a structure ofa conventional heat roller. Because the heat roller 10 shown in FIG. 1has a heat source, the heat roller 10 requires a rotating power supplyunit for supplying an external power to the heat source. In theconventional heat roller, the rotating power supply unit includeselectrodes 13 a and 14 a installed at an end cap 13 and a gear cap 14,respectively, assembled to both ends of a heat roller body 11.Connection terminals 15 electrically connect the heat source to theelectrodes 13 a and 14 a. When the gear cap 14 and the end cap 13 areloosely fastened to the heat roller, the caps 13 and 14, especially, thegear cap 14 may become unfastened, thereby resulting in twisting anddisconnecting of the connecting terminals 15 from the heat roller.Therefore, the caps 13 and 14 should be securely fastened.

FIG. 2 is an exploded perspective view of a gear cap part of a heatroller of FIG. 1. As shown in FIG. 2, the gear cap 14 generally has ascrew part 14 b that is securely fastened to a screwed hole part 11 bformed at the roller body 11. While not shown, the end cap 13 is alsofastened by a screw means.

Although the gear cap and the roller body in the heat roller of thefixing apparatus are fastened to each other, when they are backlashedthe gear cap may be separated from the roller body so that theconnecting terminals 15 for connecting the electrodes 13 a and 14 a anda resistance heater 12 may be twisted to cause disconnection. Moreover,because the roller body of the heat roller has a thickness of about 1 mmand thus a small thread height of about 0.35 mm, therefore, when theroller is subjected to a strong rotational torque, the threads may bebroken to make the gear cap skid to cause disconnection, therebyresulting in bad contact of the terminal, sparks and other detrimentalresults.

Korean Patent Registration No. 452874 discloses a heat roller of afixing apparatus for fastening a gear cap and a roller body using aseparate fastening means, without forming threads at the gear cap.

FIGS. 3 and 4 illustrate the heat roller of Korean Patent RegistrationNo. 452874. FIG. 3 is an exploded perspective view and FIG. 4 is across-sectional view thereof. Referring to FIGS. 3 and 4, a gear cap 24is fastened to an end of a roller body of a heat roller 20 using afixing ring 30 and a hooking projection 32 a. A groove 24 b in the gearcap 24 receives the fixing ring 30. The fixing ring 30 confines the gearcap 24 to the roller body 21 to prevent axial separation, and thehooking projection 32 a is inserted into a hooking groove 31 a toconfine the gear cap 24 to the roller body 21 to prevent idling when theend 31 of the roller body 21 is received in the recess 32 in the gearcap 24.

The fastening structure of the gear cap 24 has a good coherence incomparison with the conventional thread fastening structure. However, asshown in FIGS. 3 and 4, because the roller body 21 has an annular groove21 b into which the fixing ring 30 can be inserted, the roller body mayhave a low strength due to the annular grooves formed at both ends ofthe roller body 21. Even though the smaller the thickness of the rollerbody, the shorter the time required to reach a print temperature, thatis, a first print out time (FPOT), there is a limit to how much thethickness of the roller body may be reduced due to the above reasons.

Accordingly, a need exists for a fixing apparatus for an image formingapparatus in which a heat roller has an improved cap connection.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a heat roller for afixing apparatus capable of maintaining secure engagement of a rollerbody and caps using a new fastening means, without forming screw threadsor screw grooves at the roller body.

A heat roller for a fixing apparatus includes a conductive cylindricalroller body, a resistance heater installed in the roller body, and capsconnected to both ends of the roller body and respectively havingelectrodes for supplying current to the resistance heater. Fasteningmeans confine at least one cap so that the cap is prevented from beingaxially separated from the roller body and from being idled at theroller body.

The fastening means may include a fastening part projecting from a gearcap to be inserted into the roller body and having a fastening groovewith a predetermined depth on the outer surface of the roller body. Aspring key is inserted in the fastening groove and has a plurality ofprotrusions on its outer surface.

The fastening groove may be an annular groove or a polygonal groove,such as a hexagonal or octagonal groove.

The spring key is preferably formed as a semi-circular resilient keyhaving an inner surface consisting of a plurality of planes. Morepreferably, the spring key is formed as two keys installed opposite toeach other in one cap.

Preferably, the cap has an inner cap installed therein. The cap and theinner cap are fastened to each other by a fastening member, such as ascrew, a bolt or similar fastener.

A bearing may be installed at an outer surface of the roller body.

Other objects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will be describedin reference to certain exemplary embodiments thereof with reference tothe attached drawings, in which:

FIG. 1 is an elevational view in cross section of a conventional heatroller for a fixing apparatus;

FIG. 2 is an exploded perspective view of a gear cap of the heat rollerof FIG. 1;

FIG. 3 is an exploded perspective view of a gear cap of anotherconventional heat roller;

FIG. 4 is an elevational view in cross section of the gear cap of FIG.3;

FIG. 5 is an exploded perspective view of a gear cap of a heat roller inaccordance with an exemplary embodiment of the present invention; and

FIG. 6 is a partially cut-away perspective view of the assembled heatroller of FIG. 5.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features, and structures.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention is described more fully hereinafter with referenceto the accompanying drawings, in which exemplary embodiments of theinvention are shown.

FIG. 5 is an exploded perspective view of a gear cap of a heat roller inaccordance with an exemplary embodiment of the present invention. FIG. 6is a partially cut-away perspective view of the assembled heat roller ofFIG. 5.

Referring to FIGS. 5 and 6, a heat roller 100 according to an exemplaryembodiment of the present invention includes a conductive cylindricalroller body 111, a resistance heater 112 installed in the roller body,and caps 114 respectively connected to both ends of the roller body andhaving electrodes for supplying a current to the resistance heater.Fastening means 120 confine at least one cap to prevent the cap fromaxially separating from the roller body and to substantially prevent thecap from idling at the roller body.

The fastening means 120 includes a fastening part 122 projecting fromthe cap 114 to be inserted into the roller body 111 and having afastening groove 124 of predetermined depth formed at its outer surface.A spring key 121 is inserted in the fastening groove 124.

The fastening means 120 may confine a gear cap 114, an end cap, or maybe used at both ends to confine the gear and end caps. Securing the endcap is substantially similar to securing the gear cap 114, accordinglythe end cap is not shown.

The fastening groove 124 may be an annular groove, or a polygonalgroove, such as a hexagonal or octagonal groove.

The spring key 121 has a plurality of protrusions 125 at its outer edge.An inner surface of the spring key 121 has an annular shape or apolygonal shape, such as a hexagonal or octagonal shape. Preferably, theinner surface has a plurality of planes 123. The protrusions 125 mayhave various shapes, such as a triangular shape, a tooth shape, or thelike. Preferably, the protrusions have a substantially triangular shape.The spring key 121 is preferably formed to have a semi-circular shape.In an exemplary implementation, as shown in FIG. 5, the spring key isformed as two keys installed opposite to each other in one cap. Thespring key is preferably formed of a resilient material, such as steel,steel alloy, or stainless steel.

Preferably, the cap 114 has an inner cap 115 installed therein. The cap114 and the inner cap 115 are fastened to each other by fastening member117, such as a screw, a bolt or other suitable fastener. As shown inFIGS. 5 and 6, the fastening member includes a bolt 117 a inserted fromone side of the cap 111 and a nut 117 b disposed on an opposite side ofinner cap 115, thereby securing the cap 114 and the inner cap 115. Aninsulating material 114 b is provided on a side surface of the cap 114when the cap 114 is fastened to the roller body 111. The electrode 114 ais then installed on the insulating material 114 b.

A bearing 116 may be installed at a periphery of the roller body 111.

Because the heat roller 100 having the above fastening structureincludes the roller body 111 securely fastened by the spring key 121,the heat roller is not separated in an axial direction of the roller aswell as not being idled in a rotational direction.

To compare performance of the heat roller 100 according to an exemplaryembodiment of the present invention and the conventional heat roller 10(FIG. 1), a gear chuck for chucking the cap was manufactured to performa torque test of each heat roller.

As a result of the torque test, while the threads of the conventionalheat roller broke to make the roller idle, resulting in disconnection ata torque of 30˜35 kg-cm, the heat roller according to an exemplaryembodiment of the present invention was not idled at a torque of 163˜167kg-cm.

As shown by the foregoing test results, the heat roller for a fixingapparatus according to an exemplary embodiment of the present inventionis capable of more securely fastening the roller body to the caps usinga novel fastening means and therefore increasing lifespan of the heatroller because there is no disconnection of a coil and no spark betweenthe electrodes. Furthermore, because the heat roller for a fixingapparatus according to an exemplary embodiment of the present inventiondoes not use a screw means, it is possible to reduce manufacturing costsof the roller body and a first print out time (FPOT) by decreasing athickness of the roller body in comparison with the conventional art.

Although the present invention has been described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that a variety of modifications and variations may bemade to the present invention without departing from the spirit or scopeof the present invention defined in the appended claims, and theirequivalents.

1. A heat roller for a fixing apparatus, comprising: a conductivecylindrical roller body; a resistance heater installed in the rollerbody; a cap connected to one end of the roller body and respectivelyhaving an electrode for supplying a current to the resistance heater;and fastening means for confining the cap to prevent the cap fromaxially being separated from the roller body and to substantiallyprevent the cap from being idled at the roller body.
 2. The heat rollerfor a fixing apparatus according to claim 1, wherein the fastening meansincludes a fastening part projecting from the cap and having a fasteninggroove on the outer surface of the fastening part; and a spring keydisposed in the fastening groove and having a plurality of protrusionsextending outwardly from an outer edge thereof.
 3. The heat roller for afixing apparatus according to claim 1, wherein the fastening meansconfines a gear cap.
 4. The heat roller for a fixing apparatus accordingto claim 1, wherein the fastening means confines an end cap.
 5. The heatroller for a fixing apparatus according to claim 2, wherein thefastening groove is an annular groove.
 6. The heat roller for a fixingapparatus according to claim 2, wherein the fastening groove has asubstantially polygonal shape.
 7. The heat roller for a fixing apparatusaccording to claim 2, wherein the spring key is formed as asemi-circular resilient key.
 8. The heat roller for a fixing apparatusaccording to claim 2, wherein the spring key has an inner surface havinga plurality of planes.
 9. The heat roller for a fixing apparatusaccording to claim 2, wherein the spring key is formed as two keysinstalled opposite to each other in the cap.
 10. The heat roller for afixing apparatus according to claim 1, wherein the cap has an inner capinstalled therein.
 11. The heat roller for a fixing apparatus accordingto claim 1, wherein a bearing is disposed on an outer surface of theroller body.
 12. The heat roller for a fixing apparatus according toclaim 10, wherein the cap and the inner cap are fastened to each otherby a fastening member.
 13. The heat roller for a fixing apparatusaccording to claim 2, wherein the plurality of protrusions have asubstantially triangular shape.
 14. The heat roller for a fixingapparatus according to claim 12, wherein an insulating member isdisposed between the electrode and the fastening member.
 15. A heatroller for a fixing apparatus, comprising: a conductive cylindricalroller body; a resistance heater installed in the roller body; a firstcap connected to a first end of the roller body; a second cap connectedto a second end of the roller body; first and second electrodes disposedat first and second caps, respectively, for supplying a current to theresistance heater; and first and second fastening means for confiningthe first and second caps to prevent the fist and second caps fromaxially being separated from the roller body and to substantiallyprevent the first and second caps from being idled at the roller body.16. The heat roller for a fixing apparatus according to claim 15,wherein each of the first and second fastening means includes afastening part projecting from the cap and having a fastening groove onthe outer surface of the fastening part; and a spring key disposed inthe fastening groove and having a plurality of protrusions extendingoutwardly from an outer edge thereof.
 17. The heat roller for a fixingapparatus according to claim 16, wherein the plurality of protrusionshave a substantially triangular shape.
 18. The heat roller for a fixingapparatus according to claim 16, wherein the spring key is formed as asemi-circular resilient key.
 19. The heat roller for a fixing apparatusaccording to claim 16, wherein the spring key is formed as two keysinstalled opposite to each other in the cap.
 20. The heat roller for afixing apparatus according to claim 15, wherein each of the first andsecond caps has an inner cap secured thereto by a fastening member.